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Update configure line for riscv-gnu-toolchain in readme

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Luke Wren 2022-07-06 22:41:32 +01:00
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Readme.md
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@ -70,7 +70,7 @@ The [Yosys GitHub repo](https://github.com/YosysHQ/yosys) has instructions for b
## RISC-V Toolchain
The instructions below are for building a version of the 32-bit [RISC-V GNU toolchain](https://github.com/riscv/riscv-gnu-toolchain) with multilib support for the various combinations of RV32I/M/C ISAs:
The instructions below are for building a version of the 32-bit [RISC-V GNU toolchain](https://github.com/riscv/riscv-gnu-toolchain) with multilib support for the various combinations of RV32I/M/A/C ISAs:
```bash
# Prerequisites for Ubuntu 20.04
@ -78,17 +78,16 @@ sudo apt install -y autoconf automake autotools-dev curl python3 libmpc-dev libm
cd /tmp
git clone --recursive https://github.com/riscv/riscv-gnu-toolchain
cd riscv-gnu-toolchain
# The ./configure arguments are the most important difference
./configure --prefix=/opt/riscv --with-arch=rv32imc --with-abi=ilp32 --with-multilib-generator="rv32i-ilp32--;rv32ic-ilp32--;rv32im-ilp32--;rv32imc-ilp32--"
./configure --prefix=/opt/riscv --with-arch=rv32ia --with-abi=ilp32 --with-multilib-generator="rv32i-ilp32--;rv32ia-ilp32--;rv32iac-ilp32--;rv32ic-ilp32--;rv32im-ilp32--;rv32ima-ilp32--;rv32imac-ilp32--;rv32imc-ilp32--"
sudo mkdir /opt/riscv
sudo chown $(whoami) /opt/riscv
make -j $(nproc)
```
The multilib build is strongly recommended -- getting a RV32IMC standard library on a RV32I processor variant will ruin your day, and running soft float that does not use the multiply instructions is not much fun either.
This build will also install an appropriate gdb as `riscv32-unknown-elf-gdb`.
The `--with-multilib-generator=` flag builds multiple versions of the standard library, to match possible `-march` flags provided at link time. If there is no _exact_ match, the linker falls back to the architecture specified by the `--with-arch` flag, which in this case is the fairly conservative RV32IA. This will become worse with GCC 12, where for example the CSR instructions have moved from `I` to `Zicsr`, and the entire arch string must still be matched to get the non-fallback library.
## Actually Running Hello World
Make sure you have done a _recursive_ clone of the Hazard3 repository. Build the CXXRTL-based simulator: